In a PON (Passive Optical Network) based on P2MP architecture, a communication device located in a central office, such as an OLT (Optical Line Terminal), receives information reported from multiple user side devices, such as multiple ONUs (Optical Network Units), in a time division multiple access (TDMA) mode.
When the physical optical channel corresponding to each branch fiber is tested, a test device in the central office receives multiple test signals returned from different ONUs. However, the test signals generally do not carry information for identifying the corresponding branch fiber. Therefore, after receiving the multiple test signals, the test device cannot distinguish the specific branch fiber from which each test signal comes.
In view of the above problem, a method for identifying a test signal in the existing techniques is as follows: at the time of constructing a PON network, the branch fibers are ensured to have different lengths; after receiving a test signal from a branch fiber, the test device obtains a length of the branch fiber according to a transmission duration of the test signal in the branch fiber, and identifies the specific branch fiber from which the test signal comes according to the length of the branch fiber. However, this method for identifying the test signal requires that branch fibers to have different lengths at the time of network constructing the PON, which increases the difficulty of implementation.
Another method for identifying the test signal is as follows: test signals with different wavelengths are distributed for different branch fibers, and the test device identifies the specific branch fiber from which each test signal comes according to the wavelength of the received test signal. However, since the test signals are normally provided by the test device in the central office, in order to send the test signals with different wavelengths, this method has a high requirement on a tunable laser in the test device such as an OTDR (Optical Time Domain Reflectometer) in the central office, thus a cost for implementing this method is high.